A conventional scrollbar includes a thumb which can be dragged along a track to jump to specific locations in a document (e.g., a web page), for example, to provide a visual indication to a user of a current position within the document. For example, if the thumb is halfway down a scrollbar's track, it tends to indicate that the user is halfway through the content of the document. The design of conventional scrollbars is suitable for documents which contain static content, such as a predetermined page length, a predetermined number of items to be displayed, and so forth.
However, many documents today, such as web pages, dynamically update content to be displayed as the user manipulates the scrollbar, such as adding additional items when the user nears or reaches the end of currently available content. In response to receiving dynamic content, many conventional scrollbars force the position of the scrollbar's thumb to jump while the user is dragging the scrollbar thumb. Other conventional scrollbars prevent navigation to the newly added dynamic content until the thumb is released (which immediately causes the thumb's position to jump). When a mouse pointer is being used to manipulate the scrollbar, this erratic jumping of the thumb may reduce the efficiency of the user's ability to scroll, as the relative positions of the mouse pointer and thumb are jumping erratically. Similarly, the erratic jumps may cause the user to lose their place within the web page. When a user's finger is being used to manipulate the scrollbar on a touch device, this can result in erratic behavior because the user's finger remains in the original location of the thumb, which can result in large “jumps” in the displayed content when the next touch result is processed. As such, using conventional scrollbars to navigate documents with dynamically expanding content can be confusing and frustrating to users.